Enhanced superplasticity utilizing dynamic globularization of Ti-6Al-4V alloy

This study aimed to determine the optimum processing conditions for dynamic globularization of Ti-6Al-4V alloy having martensite microstructure, and to achieve enhanced superplasticity. A series of isothermal compression tests was carried out for martensite microstructure in the strain range of 0.6-1.4, the strain rate range of 10^-3 s^-1 to 1 s^-1 and the temperature range of 973-1223 K. At each test condition, a quantitative analysis was made to measure the fraction of dynamic globularization associated with fragmentation of initial lamellar structures. It was found that the dynamic globularized fraction increased with increasing strain and with decreasing strain rate and/or temperature tested. Based on the processing map and microstructural analysis, the optimum processing condition to obtain the finest equiaxed microstructure was determined. A very high elongation over ≈1000 pct was achieved at relatively high strain rate superplasticity regime (>10^-2 s^-1). The present enhanced superplasticity was rationalized by examining the microstructures of the alloy associated with dynamic globularization.